The most pertinent prior art relative to this apparatus that the applicant and his attorney are aware of is that which is to be described hereinbelow.
My associates have been making duo density rotors of silicon nitride for gas turbine engines in the following manner. A rotor blade ring is formed, for example, in an injection molding operation. This blade ring has an annular ring portion with a plurality of complex shaped blade surfaces projecting outwardly therefrom. The blade ring is formed by injection molding silicon particles in a mold suitable for forming the complex shape desired. The particles are suspended in a suitable molding vehicle. After the molding operation, the molding vehicle is burned away as is known in the art to leave behind a consolidated mass of silicon particles in the shape of the blade ring. This blade ring is subsequently subjected to a nitriding operation in which the silicon particles are converted to silicon nitride. All but an interior annular surface of the silicon nitride article is subsequently encapsulated with additional material which is transformed thereafter into silicon nitride to form a ring shaped unit. The article is encapsulated so that the blades and support portion thereof can be supported to withstand the temperatures and pressures of a hot press bonding operation in which a central hub can be simultaneously formed and bonded to an interior annular surface of the blade ring to form a duo density rotor.
The general apparatus previously used for simultaneously forming the central hub and bonding it to an interior annular surface of the blade ring is disclosed in U.S. patent application Ser. No. 571,897 filed Apr. 25, 1975 for METHOD OF FORMING A DUO DENSITY SILICON NITRIDE ARTICLE, which application is now abandoned. This application was assigned to the same assignee as this application and is hereby incorporated by reference. The apparatus disclosed in the mentioned application had several shortcomings and as a result one was unable to obtain finished articles without imperfections. The apparatus disclosed in the cited patent application did not provide sufficient means for assuring an equal distribution of the forces applied to the apparatus during the hot pressing operation.
I have developed modifications of the prior apparatus which allow the manufacture of articles essentially free of cracks. The apparatus of my invention is also efficient in operation.